Yeah, it's still in the fluff - it's just not supported by the mechanics in either MP or SP. To be honest, I'm fine with that - shields being dealt with by raw DPS makes more sense anyway, and armour needs to be punched through by a powerful weapon.

The other problem with using DR for ME armor is that it doesn't make you immune to anything.

The only thing I particularly recall Armored enemies being immune to is Concussive Shot, which is just a missile that has a whole bunch of Takedown and does more damage if you improve it. Shields and Barriers block more and different things.

I'm pretty sure they all block everything except damage. Armored enemies are immune to singularity, lift, throw, and pull for instance. Shockwave and Charge continue to do damage, but don't send them flying. Likewise with Concussive shot and Carnage. And AI Hacking/Sabotage, Cryo Blast, Dominate, Slam.

In fact, to quote the wiki on the matter:

Quote from: Mass Effect Wiki

Stasis is unique among powers in that it will work despite any defensive layers that an enemy has, with the drawback of not directly dealing damage.

The only thing Armor isn't immune to that other ME defenses are is fire, and that's because Armor is specifically weak to it, just like shields are specifically weak to Overload which has zero effect on Armor.

I set up all three ME protections as conditions that grant immunity to ME powers, a bit of protection from crits and damage, and a weakness to a specific damage type. Since they are things that can be gained and lost throughout a combat (Shields and Barriers at least, I don't think Armor regenerates in the video games), a condition seems more appropriate than an NPC quality. Eventually you would probably want to back that up with NPC qualities that grant the conditions, but that can wait.

My principle objection goes against the 10+.5*Damage save to keep a Shield or Barrier up. That's just math and extra rolling in the middle of combat. Maybe for Shields and Barriers the save DC could be Damage that adds up until the Shield/Barrier drops? Better gear can get a bonus to the roll or fail more than one save before just dropping.

In ME3, the only armoured enemies are also big. Brute, Banshee and Atlas. They have DR85 odd, which makes most weapons outright useless (think DR20 in MC terms). You could go as easy as "you add your DR to this opposed check" for things like throw / pull etc (so that players in Riot Gear type stuff are pretty resistant to all forms of attack, but are slow and have minimal Defence) or simply handwave it as "It's not armour that stops the powers, it's bulk - you just can't singularity a Brute".

I'd go with the latter, because trying to replicate that level of videogame mechanics at the tabletop adding unnecessary difficulty and changing the core tabletop mechanics too much to be worth the benefit. Like I said in the Shadowrun thread, capturing the flavour is more important here (especially when the reason for Armour stopping powers is to attempt to built a Rock-Paper-Scissors balance point in their game, so Adepts don't rule the roost*).

*Yes they failed, due to Warp-Throw being able to tear anything apart faster then any other option in the game, but the idea was balance.